Answer
Upon returning to Afghanistan, Amin joined the People's Democratic Party of Afghanistan (PDPA). The PDPA was a Marxist-Leninist party founded in 1965. It was divided into two factions: the Khalq faction, led by Amin, and the Parcham faction, led by Babrak Karmal. Amin's membership in the PDPA played a significant role in his rise to power.